The Escherichia coli ssuEADCB gene cluster is required for the utilizationof sulfur from aliphatic sulfonates and is regulated by the transcriptional activator Cbl

The growth properties of an Escherichia colt strain carrying a chromosomal deletion of the ssuEADCB genes (formerly designated ycbPONME) indicated tha t the products of this gene cluster are required for the utilization of sul fur from aliphatic sulfonates. Sequence similarity searches indicated that the proteins encoded by ssuA, ssuB, and ssuC are likely to constitute an AB C type transport system, whereas ssuD and ssuE encode an FMNH2-dependent mo nooxygenase and an NAD(P)H-dependent FMN reductase, respectively (Eichhorn, E., van der Ploeg, J. R., and Leisinger, T. (1999) J. BioL Chem 274, 26639 -26646). Synthesis of beta-galactosidase fi om a transcriptional chromosoma l ssuE'-lacZ fusion was repressed by sulfate or cystine and depended on the presence of a functional cbl gene, which encodes a LysR-type transcription al regulator, Electrophoretic mobility shift assays with the ssu promoter r egion and measurements of beta-galactosidase from plasmid-encoded ssuE'-lac Z fusions showed that full expression of the ssu operon required the presen ce of a Cbl-binding site upstream of the -35 region. CysB, the LysR transcr iptional regulator for the cys genes, was not required for expression of a chromosomal ssuE'-lacZ fusion although the ssu promoter region contained th ree CysB-binding sites. Integration host factor could also occupy three bin ding sites in the ssu promoter region but had no influence on expression of a chromosomal ssuE'-lacZ fusion.